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Putting a Rainbow Optics (RO) Spectral Filter in Front of a TelephotoLens



 
 
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  #1  
Old April 15th 08, 02:15 AM posted to sci.astro.amateur
W. Watson
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Posts: 203
Default Putting a Rainbow Optics (RO) Spectral Filter in Front of a TelephotoLens

The RO filter looks like a common 1.25" astronomical filter used on many
telescopes. What I would like to do with it is put it on the front of my
Canon 75-300mm zoom lens. I have a 67 mm UV filter on the front of lens now.
It needs to be replaced with something that will allow my to put the RO in
its place.

I think a critical accessory is what is called a camera filter step-up ring.
I've never used one, but I'm guessing it spans the gap between it and the
next adapter, which is a prime focus adapter for a 1.25 eyepiece holder. I'm
holding something like the latter in my hand. It looks like a stove pipe
hat. Not all of it is needed. The O.D. of the hat is 1.25" and it has
threads on the inside at the top. The hat is 1.375" tall. The brim is about
1.625" (40 mm?) across, and has threads on the outside. It would be very
helpful if the hat unscrewed from the brim, so only the brim could be used.
Of course, it would need threads at the top for the RO filter.

Possibly it all works like this. Take the step-up ring and replace the UV
filter. Screw into the ring the prime focus adapter (brim). Screw the RO
filter into the adapter. Anyone know where I can get the required parts, or
some other set of parts that will do the same?

--
Wayne Watson (Nevada City, CA)

Web Page: speckledwithStars.net
  #2  
Old April 15th 08, 05:04 PM posted to sci.astro.amateur
canopus56[_3_]
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Posts: 46
Default Putting a Rainbow Optics (RO) Spectral Filter in Front of a Telephoto Lens

"W. Watson" wrote in
:
snip
Anyone know where I can get the
required parts, or some other set of parts that will do the same?


Different setup, but you might want to take a look at Rick Evans imaging
train in Issue #7 of _Selenology Today_ at page 5. It uses a Rainbow
Optics grating with a Televue Powermate.

http://digidownload.libero.it/glrgro...logytoday7.pdf

The step-down ring approach is interesting. Haven't done it myself. Here
is a link to a Canon dealer with a product catalogue showing a number of
steps rings that could get you from 67mm to 49mm (T-adapter).

http://www.overlandphoto.com/pages/lensacc.html

- Canopus56


** Posted from http://www.teranews.com **
  #3  
Old April 15th 08, 05:20 PM posted to sci.astro.amateur
David Weinshenker
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Posts: 65
Default Putting a Rainbow Optics (RO) Spectral Filter in Front of a TelephotoLens

canopus56 wrote:
"W. Watson" wrote in
:
snip
Anyone know where I can get the
required parts, or some other set of parts that will do the same?


Different setup, but you might want to take a look at Rick Evans imaging
train in Issue #7 of _Selenology Today_ at page 5. It uses a Rainbow
Optics grating with a Televue Powermate.

http://digidownload.libero.it/glrgro...logytoday7.pdf

The step-down ring approach is interesting. Haven't done it myself. Here
is a link to a Canon dealer with a product catalogue showing a number of
steps rings that could get you from 67mm to 49mm (T-adapter).

http://www.overlandphoto.com/pages/lensacc.html


I thought the "T adapter" thread size was 42mm x 0.75mm
and 2" eyepiece filter threads were 49mm x 0.75 mm...

(I still haven't figured out what the nominal size for 1-1/4" eyepiece filter
threads is supposed to be...)

-dave w
 




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